Setting off firecrackers is a practice handed down from the remote past,when burning bamboo stems were burnt. Bamboo stems have joints and are hollow inside. When they are burnt,the air inside expands after being heated,and the stems themselves burst open and make a loud cracking sound. Later on, people placed gunpowder in the bamboo stems and thus invented firecrackers. Still later, paper rolls replaced bamboo stems. By the close of the Qing Dynasty,there were already special workshops in China making all kinds of firecrackers.